It is known that the anisotropy of the plastic strain ratio R(.alpha.) is an important factor in predicting forming capabilities of metal plate. Measurement of R(.alpha.) is presently obtained mostly by destructive lengthy tensile testing. The testing implies that several plate samples of prescribed shape be cut out of each plate to be tested at different angles .alpha. with respect to the rolling direction of the plate, that strain gages be placed on each sample and then that each smaple be strained and the ratio of strains be measured according to the following relationship: ##EQU1## where .epsilon..sub.w (.alpha.) is the true strain in the width direction and .epsilon..sub.t (.alpha.) is the true strain in the thickness direction. The average plastic strain R and the planar plastic strain ratio .alpha.R are then determined from the measurements of R(.alpha.). Also known in the art is a compact tester for predicting metal sheet drawability (Metal Progress, June 1985, page 47). To obtain data representative of the sheet drawability, test strips are taken from each sheet at 0.degree., 45.degree. and 90.degree. to the rolling direction. In sequence, each strip is inserted into the unit's slot, and the resonant frequency is displayed on a digital readout. The value of these resonant frequencies are manipulated to obtain an average value of Young's modulus. Then the average plastic ratio is established from an empirical relationship with the Young's modulus. Also known in the art is a method of determining the average plastic strain ratio R of sheet material of known density (U.S. Pat. No. 4,432,234, Feb. 21, 1986, Jones). The patent uses r for the average plastic strain ratio. The method comprises the steps of subjecting the sheet material to mechanical vibrations, determining an elastic property of the material which is manifest as the velocity of the mechanical vibrations which are propagated through the thickness of the sheet, and determining the value of R from a previously established empirical relationship between the said elastic property and R. Although all the above methods are suitable for estimating forming capabilities of metal plate, none of these methods can estimate the forming capabilities of metal plate with a high degree of precision by a rapid and non destructive technique.
There is a need for a method of, and an apparatus for, evaluating forming capabilities of a metal plate, with a degree of precision never achieved before, by a rapid and non destructive technique.
There is also a need for evaluating the angular variation of plastic strain ratio R (.alpha.) of a metal plate, with a degree of precision never achieved before, by a rapid and non destructive technique.
There is also a need for evaluating the average plastic strain ratio R of a metal plate, with a degree of precision never achieved before, by a rapid and non destructive technique.
There is also a need for evaluating the planar strain ratio .DELTA.R, with a degree of precision never achieved before, by a rapid and non destructive technique.